The present invention relates to a developer solution for positive-type photoresists or, more particularly, to a developer solution for positive-type photoresists which is usable in the development treatment of a photoresist, without any limitations concerning temperature dependencies of the sensitivity and the solubility of the unexposed photoresist material in the solution.
As is well known, the photolithographic process using a photoresist material is widely practiced in the manufacture of semiconductor devices, printed circuit boards, printing plates and the like products with an object to provide image-wise protection to the surface of the substrate, which is subjected to a surface treatment such as etching, metal plating and diffusion. The photoresist process is performed by use of a photoresist material, or merely resist, which is a resinous organic polymer having photosensitivity, and the process comprises the steps of coating the surface of the substrate uniformly with the photoresist, followed by heat treating the surface to provide a photoresist layer thereon, exposing the photoresist layer to ultraviolet light image-wise or pattern-wise, for example, through a photomask mounted thereon so as to produce a difference in the solubility of the photoresist between the exposed and unexposed areas, developing the photoresist layer to form a pattern of the photoresist by partially removing the photoresist material from the areas where the photoresist has a larger solubility, and subjecting the thus-exposed patterned portions of the substrate to a subsequent treatment.
Photoresist materials in general can be classified as the so-called negative and positive-types. In the negative-type photoresist materials, the resin is cured by irradiation with light so that the photoresist on the unexposed areas can be dissolved and removed away by a developer solution used in the development to leave a pattern-wise photoresist layer on the exposed areas. On the other hand, the solubility of the positive-type photoresist resin is increased by the irradiation with light to such an extent that the developer solution can dissolve away the photoresist on the areas exposed to light, leaving a pattern-wise photoresist layer on the unexposed areas. Generally, positive-type photoresists are preferred over negative-type ones because they provide higher sharpness and larger resolving power of the images, have an insusceptibility to influence of atmospheric oxygen in the course of exposure to light, and have a stability of the photoresist layer formed on the substrate surface by coating.
The photosensitive resins in most of the positive-type photoresists currently available on the market contain naphthoquinone diazide which provide the photosensitive groups, and the photoresist typically comprises an alkali-soluble novolac resin and an ester of a naphthoquinone diazide compound and a phenolic compound or a polymer having phenolic hydroxy groups as a sensitizer. When irradiated with light, the quinone diazide group in the positive-type photoresist as described above is photochemically decomposed to form an indene carboxylic acid through an indene ketene which is soluble in alkali so that the photoresist is dissolved by reaction thereof with an organic or inorganic alkali. Thus, the developer solution used in the development of a positive-type photoresist is usually an aqueous alkali solution which dissolves the alkali soluble acid produced from the photoresist by the photochemical reaction.
The alkaline developer solution of the most conventional type is an aqueous solution containing sodium metasilicate, sodium hydroxide or sodium phosphate as the principal ingredient. Such an alkaline developer solution, however, cannot be used in the manufacturing process of semiconductor devices, for example, the formation of a pattern-wise photoresist layer on a semiconductor silicon wafer, because alkali metals including sodium are the most detrimental impurities in semiconductors.
Accordingly, the developer solution widely used in semiconductor processing is an aqueous alkaline solution containing a quaternary ammonium salt or a mixture of an amine and an alcohol and the like organic base. A problem in a developer solution of this type is that it has a remarkable temperature dependency on the sensitivity of the photoresist, so that difficulties are encountered in the control of the line width of the photoresist pattern in the course of the development treatment. The difficulty in the line width control is particularly large in the spray development because evaporation of the solvent from the sprayed developer solution necessarily causes a considerable temperature decrease of the solution. As a consequence, the photoresist pattern is poor in the sharpness of the image with unsatisfactory reproducibility, so that development treatments with such a developer solution must be performed by controlling the temperature of the solution usually within .+-.1.degree. C. of the recommended temperature for the development.
Thus, it has been eagerly desired to develop a developer solution for a positive-type photoresist free from the above described limitation concerning the requirement for the exact temperature control of the developer solution.